The invention relates to a method and a device for melting down solid combustion residues
In the disposal of waste in combustion installations, ashes, slags and filter dusts arise which, as a result of the conventionally prevailing combustion temperatures of 850.degree. to 1050.degree. C., are present only in crystalline or in sintered form. These combustion residues contain heavy metals, salts and harmful organic substances so that almost exclusively dumping is available for disposal. Grate ashes and grate slags are at present stored on domestic refuse and mono-dumps unless they find use to a limited extent as low-grade building materials. Boiler ash and fine dusts have to be stored on special waste dumps. By the action of rainwater or groundwater, the heavy metals, salts or harmful organic substances are dissolved and can penetrate uncontrollably into the groundwater. Dump spaces becoming constantly scarcer on the one hand and the sharpening of legal provisions on the avoidance and utilization of combustion residues on the other hand require a significant improvement of their chemical and physical properties.
As a result of these problems, a large number of physical, chemical and thermal treatment methods, such as e.g. compaction methods, washing methods, building-material manufacturing methods, low-temperature methods and melting methods, have already been developed.
These previously known methods solve the problems described only incompletely, such as e.g. the physical and chemical methods, or necessitate high expenditure on apparatus and energy.
It is known that in general the melting methods bring about the most lasting improvements of the properties of the combustion residues. As a result of the transfer of the combustion residues of the waste combustion installations into the molten phase, harmful inorganic substances are either bound in a leach-proof manner into a glass matrix or removed from the melt. Harmful organic substances are completely destroyed as a result of the high temperatures of 1300.degree. to 1500.degree. C.
A previously known melting method is based on the melting-down of the combustion residues from waste combustion installations in a melting tank heated with fossil energy.
In this connection, it is necessary beforehand to remove the ferruginous metal scrap completely from the hot combustion residue in order to avoid damage to the refractory lining of the melting tank. The costly magnetic separation of the ferruginous metal scrap allows, for technical reasons, a maximum temperature of only approximately 300.degree. C. The cooling of the combustion residues necessary as a result in the wet slag-remover causes an approximately 30% greater energy consumption during melting-down.
The melting-down of hot ferruginous combustion residues is in principle possible with an electric arc or plasma melting method using valuable electrical energy and with a greater portion of energy costs per ton.
On the other hand, economical primary energies are used in the melting methods with fossil energy. For reasons of energy saving, the melting-down of the combustion residues in the hot state directly after the combustion in waste combustion installations would also be desirable in melting methods with fossil energy.